Coated abrasives, considered the premier tool for abrading and finishing wood and wood-like materials, unfortunately suffer from the generation of static electricity curing their use. Static electricity is generated by the constant separation of the abrasive product from the workpiece and the machinery support for this abrasive product. This static charge is typically on the order of 50 to 100 kilovolts.
Static electricity is responsible for numerous problems. For example, a sudden discharge of the accumulated static charge can cause injury to an operator in the form of an electrical shock or can ignite wood dust particles, which poses a serious threat of fire or explosion. The static charge also causes the sawdust to cling to various surfaces, including that of the coated abrasive, the abrading machine, and the electrically non-conductive wood workpiece, thereby making it difficult to remove by use of a conventional exhaust system.
If the static electrical charge is reduced or eliminated, the coated abrasive can have a significantly longer useful life and the potential for the above-mentioned hazards can be eliminated or reduced.
Many attempts, with varying degrees of success, have been made to solve the static electricity problem. One common approach has been to incorporate an electrically conductive or antistatic material into the coated abrasive construction to eliminate the accumulation of electrical charge.
For example, U.S. Pat. No. 3,163,968 (Nafus) discloses a coated abrasive article having a coating comprising graphite on the surface opposite the abrasive material. U.S. Pat. No. 3,168,387 (Adams) discloses a coated abrasive having metal leaf pigment over the abrasive grains. U.S. Pat. No. 3,377,264 (Duke) discloses an electrically conductive layer such as a metal foil, overlying the front surface of a coated abrasive.
U.S. Pat. No. 3,942,959 (Markoo et al.) teaches a coated abrasive construction having an electrically conductive resin layer sandwiched between two electrically nonconductive resin layers to prevent the accumulation of electrostatic charge during grinding. In the latter construction, the resin layer is made electrically conductive by incorporating into the resin an electrically conductive filler which may be a metal alloy, metal pigment, metal salt or metal complex. Further, Markoo et al. conclude that in order for the electrically conductive layer to have the desired anti-electrostatic effect, it is essential that the layer not be in direct contact with the support member of the abrading machine employed.
U.S. Pat. No. 3,992,178 (Markoo et al.) discloses a coated abrasive article having an outer layer comprised of graphite particles in a bonding resin which reduces the electrostatic charges generated during grinding.
U.S. Pat. No. 5,061,294 (Harmer et al.) assigned to the assignee of the present application teaches a coated abrasive that is rendered conductive by the addition of a doped conjugated polymer.
U.S. patent application Ser. No. 07/551,091, filed Jul. 16, 1990 as a continuation-in-part of U.S. patent application Ser. No. 07/495,458, filed Mar. 16, 1990, which in turn is a continuation-in-part of U.S. patent application Ser. No. 07/396,513, filed Aug. 21, 1989 (Buchanan) assigned to the assignee of the present application, discloses including carbon black aggregates in the coated abrasive bond system. The presence of the carbon black aggregates reduces the buildup of static electricity generated during abrading.
While at least some of these references provide a solution to the static electricity problem, none provides the more convenient solution of the present invention.